Switched-mode power converters are very popular in power applications because of their high efficiency. Often, a limitation in these switched-mode power converters is their bandwidth, which is usually limited to about 1/10 of the switching frequency. In order to maximize the bandwidth, a fast wide band current control loop is generally nested inside a slower narrow band voltage control loop.
Depending on the converter dimensioning, the ripple in the current waveform can be large. The current control loop must then have enough rejection so that the ripple at the modulator's input is small enough. Simply dimensioning for the required attenuation at a switching frequency may not work, since this may also result in a current control loop with very limited bandwidth. Whilst this corresponds to averaging over a long period of time, e.g. more than a few ten of switching periods of the converter, it is desirable to average over short periods of time, preferably in the order of the switching period of the converter. Conventional solutions for processing a current waveform with large ripples yield an average current waveform with a certain delay with respect to the actual current waveform. This delay restricts the bandwidth of the current control loop.
WO 2007/107919 A1 describes a supply circuit comprising an inductor coupled to switching means and comprising a capacitor that is provided with an impedance located between the inductor and the capacitor, with a current injector and with a feedback loop comprising a converter for controlling the current injector for compensating a ripple in an output voltage across the capacitor. The impedance allows injection of a compensating current at a location different from an output location.
HYUN-HEE PARK ET AL: “A fully integrated wide-band PIO controller with capacitor-less compensation for step-down DC-DC converter”, CIRCUITS AND SYSTEMS (ISCAS), 2011 IEEE INTERNATIONAL SYMPOSIUM ON, IEEE, 15 May 2011, pages 506-509 discloses how a fully integrated wide-band PID controller is implemented for a buck DC-DC converter operating in voltage mode.
KR 2014 0018488 A discloses a buck converter which uses a sensor for detecting the instantaneous value of the inductor current.
US 2013/015830 discloses alternative ways of detecting the inductor current in a buck converter.